Electric heating element



April 22, 1930. K. c. M NABB 1,755,929

ELECT-RI 0 HEAT ING ELEMENT Filed Feb. 20 1929 mvarrroz; KEITH C. MACNABB.

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ATTORNEYS.

Patented Apr. 22, 1930 UNITED STATES PATENT OFFICE KEITH CHARLES MACNABB, OF CARLETON PLACE, ONTARIO, CANADA, ASSIGNOR TO FINDLAY BROS. CO. LIMITED, 0F CARLETON PLACE, ONTARIO, CANADA ELECTRIC HEATING ELEMENT Application filed. February 20, 1929.

This invention relates to electric heating elements, and especially to those of the en closed type.

The invention has for its object to provide several improvements in electric heatlng elements whereby the construction is simplllied and strengthened and rendered more compact and economical. An lmportant object is to provide an improved structure which will be better able to withstand the stresses due to expansion and contraction produced by variations of temperature.

With these objects in view the lnvention consists in the construction, combination and arrangements of parts hereinafter described and more particularly described in the appended claims.

Referring now to the accompanying drawings which illustrate, by way of example, one convenient embodiment of the invention Figure 1 is an inverted plan view with the lower enclosing member removed,

Figure 2 is a sectional elevation on the line 22 of Figure 1, and

Figure 3 is a plan view of a pair of the grooved sectors which carry and insulate the resistance wires.

The numeral 1 indicates a circular metal heating plate on which the utensils to be heated are placed. The plate 1 is provided at its periphery with a downwardly extending flange 2 and at its centre with a boss 3. The plate 1 is also formed with a plurality of outwardly extending radial ribs 4 which are connected to the boss 3 but spaced from the flange 2, and a similar number of in wardly extending radial ribs 5 which are connected to the flange 2 but spaced from the boss 3. The ribs 4 and 5 are arranged alternately and are preferably spaced equal distances from one another. The ribs, with the flange 2, thus form a plurality of shallow, sector-shaped compartments, each compartment communicating with the next adjacent the boss 3 on one side and adjacent the flange 2 011 the other. Three inwardly projecting and three outwardly projecting ribs are shown in the drawing, but it will be understood that any suitable number of radial ribs may be employed.

Serial No. 341,455.

The heating or resistance wires, which may be of any convenient form, are mounted in grooves 6 formed in sector-shaped blocks 7 of any suitable kind of refractory insulating material, the resistance wires being indicated at 8 in Figure 2. The blocks are preferably recessed, as at 9, on one side to accommodate the ribs 4 and at 10 on the other side to accommodate the ribs 5. The blocks thus have projecting portions 11 which extend to the spaces between the ends of ribs 4: and the flange 2, and projecting portions 12 which extend into the spaces between the ends of ribs 5 and the boss 3. Alternate blocks are therefore identical and only two shapes of blocks are required. Small projections 13 maybe .formed on the blocks 7 to overhang the grooves 6 at suitably spaced points to retain the resistance wires in position.

The required number of blocks are arranged in disc-like formation, the wires are inserted in the grooves 6, and the blocks are then positioned in the compartments of plate seen from Figures 1 and 2, the ends of the grooves 6 in each block register with ends of the grooves 6 in the adjacent blocks, so that the illustratedform of the invention in eifect provides two substantially continuous, tortuous, grooves extending around the series of blocks.

The bloclrs'may be held in place by any suitable means. For example, a pad of insulating material 14 may be placed against the under side of the blocks, and retained in position by means of a dished plate 15. The rim of the plate 15 engages a recess in the flange 2 and is held detachably in position by means of a nut 16 on a central bolt 17 .mounted in the boss 3.

The ends of the resistance wires may be passed out from the grooves 6 through holes in the blocks and the pad 14:, and attached to any convenient arrangement of terminals carried by an insulating block (not shown) which may be mounted in an aperture such as 18 in the plate 15.

The invention provides a simple, strong, compact and convenient structure. The ribs 4; and 5 impart thenecessary mechanical i as shown in Figures 1 and 2. Aswill be strength to the plate 1 to enable it to Withstand the stresses produced by expansion and contraction caused by variation of temperatures. The ribs also act as partitions and aid in the formation of the compartments for containing the blocks 7. The small sector-shaped blocks are better able than a large one-piece block to withstand the stresses set up by expansion and contraction, and are more economical to manufacture and replace.

Moreover, it will be seen that if any condition arises to cause damage or breakage, such damage will usually be confined to one of the grooved blocks. That is to say, the breakage 'or warping of one or more blocks does not affect the remaining blocks.

The foregoing description and accompanying drawings are given by way of example and it will be understood that various modifications may be made without departing from the scope of the invention as defined in the appended claims.

I claim:

1. In an electric heating element, a substantially sector-shaped block of refractory material having open-ended grooves formed on. one side thereof, the grooves in said blocks opening at one end on one side of said block Adjacent the apex thereof while the other ends of said grooves open on the other side of said block adj acent'the arcuate end thereof.

2. In an electric heating element a plurality of substantially sector-shaped, grooved insulators, the grooving in each insulator being arranged to register at one end with the grooving in the adjacent insulator on one side at a point near the apex of the in iaulator, and atthe other end to register with the insulator on the other side at a point near the arcuate end of the insulator.

v3. An electric heating element comprising a heating plate,an integral, peripheral flange on said plate, a series of integral radial ribs on said plate extending inwardly from said flange and terminating at a distance from the centre of said plate, a series of ribs alternating with said first mentioned series and extending outwardly from the centre of said plate and terminating at a distance from said flange, and sector-shaped grooved insulators to fit in the compartments defined by said ribs and flange, said insulators being recessedto accommodate the ribs on each side thereof.

4. An electric heating element as claimed in claim 3, wherein each of said insulators is formed with a plurality of tortuous grooves which open at one end adjacent the apex on one side of the insulator and open at the other end adjacent the arcuate end on the other side of the insulator.

In testimony whereof I have afiixed my signature.

-KE'ITH CHARLES MACNABB. 

